In general optical measurement such as spectroscopic measurement and voltage measurement, a ratio between a physical quantity x0 and a physical quantity x1 is determined. The spectroscopic measurement for example refers to measurement of wavelength dependency of optical properties of a measurement target sample through determination of a ratio between an intensity (physical quantity x1) of light that has interacted with the sample (typically, light transmitted through the sample) and an intensity (physical quantity x0) of light that has not interacted with the sample. The voltage measurement for example refers to measurement of a ratio between a reference voltage (physical quantity x0) and a measurement voltage (physical quantity x1).
Consider now the case where temporal variation of the physical quantity x0 and the physical quantity x1 is negligible as against the time required for the measurement, that is, the case where a random error can be reduced by any amount by averaging. When a ratio between the physical quantity x0 and the physical quantity x1 is to be determined precisely, improvement of precision of the measurement may be difficult due to non-linearity of a measuring device, that is, non-linearity of a relationship between measured amounts and measurement results. That is, measurement results include a non-linearity error. The non-linearity error refers to an error that occurs due to non-linearity of the measuring device.
Generally, multipoint calibration is performed in order to reduce influence of non-linearity of the measuring device. Regarding optical measurement, for example a light measuring apparatus described in Patent Literature 1 performs multipoint calibration. Specifically, the light measuring apparatus includes a calculation controlling circuit, a light receiving sensor array, and correction light emitting diodes (LEDs). The correction LEDs irradiate light onto the light receiving sensor array. The calculation controlling circuit calculates correction values at a plurality of known illuminance levels based on sensor output levels expected at the respective illuminance levels and actual sensor output levels while successively turning the correction LEDs on at the illuminance levels. At the time of an actual light measurement, the calculation controlling circuit corrects each sensor output level using a corresponding correction value. As a result, influence of non-linearity of the measuring apparatus is reduced. Regarding voltage measurement, for example multipoint calibration of a voltage ratio is performed by a voltage source including a Josephson device.